How can I kindly tell a classmate they have body odour?

Assalamu alaykum - I go to morning class and for about four months a female classmate who sits beside me has had a strong smell. We're not close, more like people who say hi and bye; we've known each other since middle school though. I'm literally writing this in the bathroom right now because the smell was so strong I needed air. I've noticed others' reactions too and it looks uncomfortable. I don't gossip, but watching people's expressions is upsetting. She's such a lively, helpful person with a good heart and she'd help anyone who asks. I really don't want to embarrass her. This is our last year of high school and I might not see her in college, so I want to be kind and honest. I'm not confrontational, and this bothers me, but maybe she doesn't have people around who would tell her these things. I want to assume the best of people. How can I bring it up gently so I don't hurt her feelings? I'd prefer to say it in private, respectfully, and maybe offer help if she needs it. Should I mention it in passing after class, or wait for a quiet moment? Any advice on words to use or what to avoid would be really appreciated. Update: I couldn't tell her today - she left after class and I had another period. I'm trying to build the courage to speak to her tomorrow.